Abstract Detail

Life Cycle Matters: Divergent Patterns of Community Structure Between Fern Sporophytes and Gametophytes.

Ferns and lycophytes are unique among vascular plants in that their sporophyte (diploid) and gametophyte (haploid) phases are largely nutritionally independent. Owing to the highly cryptic nature of fern gametophytes, ecological studies of ferns generally include only sporophytes. However, it is important to also survey gametophytes, which have the potential to differ from sporophytes in range and ecological niche, to better understand the processes that generate local fern diversity. Here, we report the results of our survey including both sporophytes and gametophytes of the ferns of the islands of Moorea and Tahiti (French Polynesia). We first constructed a comprehensive DNA barcode library (plastid rbcL and trnH–psbA) for the two island floras including 144 fern species. We then used these DNA barcodes to identify more than 1300 field-collected gametophytes from 25 plots spanning an elevational gradient from 200 to 2000 m. We found that species richness of fern sporophytes peaks at mid-elevations, and that fern sporophyte communities become increasingly phylogenetically clustered at higher elevations. In contrast, species richness of fern gametophytes is consistent across sites, and gametophyte communities are more phylogenetically diverse than sporophytes. These results are consistent with recent studies indicating that fern gametophytes have greater physiological tolerances than sporophytes, which likely enable them to occupy a broader range of ecological niches. Our study highlights the importance of including diverse life history stages in surveys of community structure, and has important implications for our understanding of the role that gametophytes play in fern ecology.